Ascidian sperm activating and attracting factor: Importance of sulfate groups for the activities and implication of its putative receptor

The sperm activating and attracting factor (SAAF) from the eggs of the ascidian Cionaintestinalis was identified as the sulfated polyhydroxysterol,3α,4β,7α,26-tetrahydroxy-5α-cholestane-3,26-disulfate. We present a functional analysis of SAAF derivatives that reveals the roles of the various SAAF functional groups. Optical isomerism does not affect SAAF activities. Hydrolysis on one side, i.e. at the sulfate groups of SAAF, decreases the sperm-activating and sperm-attracting activities, while hydrolysis on both sides resulted in the loss of both activities. Biotinylated-SAAF lost its sperm-activating ability, but retained sperm-binding and chemotactic abilities. Thus, the sulfate groups of SAAF are responsible for these activities.